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 From the Breastcancer.org
Why do women get breast cancer?
Just being a woman is the biggest risk factor for
developing breast cancer. There are about 266,120 new cases of
invasive breast cancer and 63,960 cases of non-invasive breast
cancer this year in American women. While men do develop breast
cancer, less than 1% of all new breast cancer cases happen in men.
Approximately 2,550 cases of breast cancer will be diagnosed in
American men this year.
The biggest reasons for the difference in breast cancer rates
between men and women are:
Women's breast development takes 3 to 4 years and is usually
complete by age 14. It's uncommon for men's breasts to fully form --
most of the male breasts you see are fat, not formed glands.
Once fully formed, breast cells are very immature and highly active
until a woman's first full-term pregnancy. While they are immature,
a women's breast cells are very responsive to estrogen and other
hormones, including hormone disrupters in the environment.
Men's breast cells are inactive and most men have extremely low
levels of estrogen.
So hormonal stimulation of highly responsive and vulnerable breast
cells in women, particularly during the extra-sensitive period of
breast development, is why breast cancer is much more common in
women than in men.” -----
From the American Cancer Society
How Does Breast Cancer Start?
Changes or mutations in DNA can cause normal breast cells to become
cancer. Certain DNA changes are passed on from parents (inherited)
and can greatly increase your risk for breast cancer. Other
lifestyle-related risk factors, such as what you eat and how much
you exercise, can increase your chance of developing breast cancer,
but it’s not yet known exactly how some of these risk factors cause
normal cells to become cancer. Hormones seem to play a role in many
cases of breast cancer, but just how this happens is not fully
understood. Inherited versus acquired DNA
mutations
Normal breast cells become cancer because of changes (mutations) in
DNA. DNA is the chemical in our cells that makes up our genes. Genes
have the instructions for how our cells function. Some DNA mutations
are inherited or passed to you from your parents. This means the
mutations are in your cells when you are born and some mutations can
greatly increase the risk of certain cancers. They cause many of the
cancers that run in some families and often cause cancer when people
are younger.
But most DNA changes linked to breast cancer are acquired. This
means the change takes place in breast cells during a person's life
rather than having been inherited or born with them. Acquired DNA
changes take place over time and are only in the breast cancer
cells.
Mutated DNA can lead to mutated genes. Some genes control when our
cells grow, divide into new cells, and die. Changes in these genes
can cause the cells to lose normal control and are linked to cancer.
Proto-oncogenes
Proto-oncogenes are genes that help cells grow normally. When a
proto-oncogene mutates (changes) or there are too many copies of it,
it becomes a "bad" gene that can stay turned on or activated when
it’s not supposed to be. When this happens, the cell grows out of
control and makes more cells that grow out of control. This can lead
to cancer. This bad gene is called an oncogene.
Think of a cell as a car. For the car to work properly, there need
to be ways to control how fast it goes. A proto-oncogene normally
functions in a way that’s much like a gas pedal. It helps control
how and when the cell grows and divides. An oncogene is like a gas
pedal that’s stuck down, which causes the cell to divide out of
control.
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Tumor suppression genes
Tumor suppressor genes are normal genes that slow down cell division
(cell growth), repair DNA mistakes, or tell cells when to die (a
process known as apoptosis or programmed cell death). When tumor
suppressor genes don't work properly, cells can grow out of control,
make more cells that grow out of control, and don't die when they
should, which can lead to cancer.
A tumor suppressor gene is like the brake pedal on a car. It
normally keeps the cell from dividing too quickly, just as a brake
keeps a car from going too fast. When something goes wrong with the
gene, such as a mutation, the “brakes” don’t work and cell division
can get out of control.
Inherited gene changes
Certain inherited DNA mutations (changes) can dramatically increase
the risk for developing certain cancers and are linked to many of
the cancers that run in some families. For instance, the BRCA genes
(BRCA1 and BRCA2) are tumor suppressor genes. When one of these
genes changes, it no longer suppresses abnormal cell growth, and
cancer is more likely to develop. A change in one of these genes can
be passed from a parent to a child.
Women have already begun to benefit from advances in understanding
the genetic basis of breast cancer. Genetic testing can identify
some women who have inherited mutations in the BRCA1 or BRCA2 tumor
suppressor genes (or less commonly in other genes such as PALB2, ATM
or CHEK2). These women can then take steps to reduce their risk of
breast cancer and make plans to look for changes in their breasts to
help find cancer at an earlier, more treatable stage.Since these
mutations in BRCA 1 and BRCA 2 genes are also associated with other
cancers (besides breast), women with these mutations can also
consider early screening and preventive actions for other cancers.
Mutations in tumor suppressor genes like the BRCA genes are
considered “high penetrance” because they often lead to cancer.
Although many women with high penetrance mutations develop cancer,
most cases of cancer (including breast cancer) are not caused by
this kind of mutation.
More often, low-penetrance mutations or gene variations are a factor
in cancer development. Each of these may have a small effect on
cancer occurring in any one person, but the overall effect on the
population can be large because the mutations are common, and people
often have more than one at the same time. The genes involved can
affect things like hormone levels, metabolism, or other things that
impact risk factors for breast cancer. These genes may cause much of
the risk of breast cancer that runs in families.
Acquired gene changes
Most DNA mutations related to breast cancer take place in breast
cells during a woman's life rather than having been inherited. These
acquired mutations of oncogenes and/or tumor suppressor genes may
result from other factors, like radiation or cancer-causing
chemicals. But so far, the causes of most acquired mutations that
could lead to breast cancer are still unknown. Most breast cancers
have several acquired gene mutations.
Tests to spot acquired gene changes may help doctors more accurately
predict the outlook (prognosis) for some women with breast cancer.
For example, tests can identify women whose breast cancer cells have
too many copies of the HER2 oncogene. These cancers tend to grow and
spread faster. There are drugs that target these cancer cell changes
and improve outcomes for patients.
[Text from Breastcancer.or and the
American Cancer Society] |
